Elephant 'GPS' keeps families together

Call it a global positioning system for elephants. Their powerful rumbles - mostly too low in pitch for humans to hear - keep family members from wandering too far, new research suggests.

African elephants form tightly knit families centred around dominant females. Family members spread out while looking for food but always reunite, says Katherine Leighty, a behavioural ecologist at Disney's Animal Kingdom in Lake Buena Vista, Florida, who led the new study.

For this reason, Leighty and her colleagues studied five captive elephants living in 4-hectare outdoor enclosure within a wildlife sanctuary owned by Walt Disney. "They're not related by blood," she says, yet "some of them seemed to have formed social bonds."

The researchers, including bioacoustic scientist Joseph Soltis, attached microphone collars to each elephant, along with a satellite tag. This allowed the scientists to sync the movements of each animal in response to a rumble.

Informative calls

After one elephant rumbled, another moved closer to it, the team found. If the two elephants were good friends - determined by how often they stuck together - and the second elephant rumbled back, the elephants moved even closer to one another, compared to less convivial pairs.

"Everybody knows that this is how the [rumbles] function, but this really proves it in a really clear way," says Mya Thompson, a behavioural ecologist at Cornell University in Ithaca, New York, who also studies African elephant communication.

But the elephant "GPS" requires each animal to have a unique call. "We haven't really nailed down precisely what structures in the calls allow animals to distinguish familiar callers from unfamiliar callers," she says. "We know they can do it, but we're not presently sure how."

The rumbles almost certainly convey information besides "here I am" or "come hither", Soltis adds. When less chummy elephants got too close, rumbles seemed to push them apart. The researchers have also found that subordinate elephants raise the pitch of their rumbles in response to the calls of dominant animals.

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